The goal of the application is a comprehensive study to perfect pars plana vitreous surgery in varius areas. A. Development of instrumentation such as an airtight cannula system for interchangeability of instruments, improvement of vitreous scissors, design of biopsy forceps for retrieval of vitreous, improvement of the operating microscope by incorporating an intraocular photographic system and an improved stereo observation system for the assistant. B. Inhibition intraocular proliferation of scar tissue as it is found in massive periretinal proliferation and after injury. Corticosteroids are intravitreally injected. Effectiveness and nontoxicity of the drug has been demonstrated previously but dosage, timing of application, use of vehicles and side effects on other healing processes in the eye have to be evaluated in animal experiments. C. Evaluation of the possible reversible retinal toxicity of intravitreally injected blood in animal experiments. Once the amount of blood and the time needed to extinguish and ERG is established vitrectomy will be performed and eyes will be monitored for possible recovery of the ERG. Morphologic changes of blood toxicity and their recovery will be studied. D. Subretinal hemorrhages in animal eyes and their absorption and effect on the retina studied by electron microscopy. A technique for surgical removal of the subretinal blood is proposed. E. Examination of biopsy specimens of membranes and pathological vitreous taken from the human eye during the course of vitreous surgery histologically, electron microscopically, and with scanning electron microscopy for morphological characteristics. Tissue cultures and immunofluorescent techniques are added to get information about the origin of participating cells.